This invention relates to a heat radiating sheet body and more specifically to a very safe heat radiating sheet body which does not show any change of resistance value even when a temperature rises due to supply of electrical power and keeps radiating temperature constant.
A heat radiating sheet body has been manufactured by the following methods.
a. A basic cloth is coated or impregnated with a conductive paint. PA1 b. A basic cloth is woven with a fabric conductive material. PA1 c. A conductive material, such as copper tape, is fixed to a basic cloth using a sewing machine.
However, the method (a) has the disadvantage that it is very difficult to coat or impregnate the basic cloth with a conductive paint in the uniform thickness, thickness of paint coated on the cloth becomes uneven, thereby an electrical resistance value is not uniform generating fluctuation for each product and the yield of product becomes low.
Meanwhile, the methods (b) and (c) bring about increase of price due to complicated manufacturing process and are not suited for mass-production.
Particularly, a heat radiating sheet body manufactured by such existing methods (a) to (c) shows drop of electrical resistance value when it is heated through supply of electrical power, increase of electrical resistance value when it is cooled because suspension of electrical power supply and therefore easily tends to increase the amount of electrical power supplied more and more with a temperature rise due to the electrical power supply.
Accordingly, unless a temperature control apparatus is particularly provided, not only it is difficult to maintain a heat radiating sheet body to a certain temperature but also abnormal temperature rise or drop may be brought about.
Particularly when a combustible material such as synthetic resin film, synthetic fiber or woven material of natural fiber is used as the basic cloth, it has always been accompanied by a controversial problem that it cannot be free from the risk of firing under abnormal temperature rise condition and it lacks in the safety.